The present invention relates to a liquid-vapor contact column in which one or more beds of structured packing is located within a column shell. More particularly, the present invention relates to such a column in which the structured packing is arranged in a plurality of vertical stacks. Even more particularly, the present invention relates to such a column in which liquid migration is inhibited between the vertical stacks in a transverse, horizontal direction of the column shell to promote constant liquid and vapor flow characteristics through each of the vertical stacks of structured packing.
In any packed column, under certain operating conditions, channeling will occur which will result in lower than expected packing performance. Packing, either random or structured, promotes liquid-vapor contact of liquid and vapor phases of a mixture to be separated. A film of the liquid phase descends through the packing while the vapor phase ascends through the packing to contact the liquid phase. In order for the packing to exhibit a projected separation performance, given by the height of packing per theoretical plate or HETP, the descending liquid and vapor flows must be uniform throughout the packing. During channeling, the uniformity of the downward flow of liquid or the upward ascent of vapor is interrupted.
It is known in the art that the potential for channeling can be reduced by segregating the packing into individual, smaller staggered columns that are located within a larger column. This is shown in U.S. Pat. No. 3,402,105 which addresses liquid channeling down the column walls. In this patent, each bed is formed by a stacked honeycomb structure in which each cell of the honeycomb is laterally staggered from a cell located either directly above or below such cell. The cells are filled with random oriented packing. As liquid descends through the packing, it sufficiently spreads out through the packing to contact the wall of each cell. The staggering of the cells ensures that liquid having contacted the walls of the cell will drop into packing contained within a honeycomb located directly below. While the staggering prevents liquid which has contacted the wall of a cell from continuing to flow along that wall, it permits the lateral migration of liquid across the full width of the column. Thus, if a vapor channel begins to form, for any reason, liquid can still be forced away from the vapor channel. As such, liquid flows are greater near the periphery of the column than in central locations of the column. While the division of the column into smaller columns will tend to inhibit channeling, the spreading liquid flow will create non-uniform flow characteristics through these sub-columns. As a result, liquid channeling while inhibited is not prevented.
As will be discussed, the present invention provides a liquid-vapor contact column in which liquid channeling is inhibited to a greater extent than prior art apparatus.